Lipoprotein triglyceride fatty acid uptake by the myocardium depends upon lipoprotein lipase activity located on the luminal surface of capillary endothelium. However, the enzyme must be synthesized, activated and secreted in or by a cellular component of the heart before it can perform its known function. Lipoprotein lipase activity fluctuates depending on nutritional and endocrine status but the regulatory mechanisms which mediate this enzyme in the heart are not understood. The purpose of the studies presented in this porposal are: (1) to determine lipoprotein lipase activity in isolated adult heart muscle cells (myocytes) and compare this activity to that in the intact heart, (2) to determine if changes in total heart and intracellular lipoprotein lipase are manifested in isolated heart myocytes, and (3) to determine the conditions which effect the secretion of lipoprotein lipase from isolated heart myocytes. A long range goal of this research program is to define the intracellular mechanisms which alter synthesis, activation or secretion of lipoprotein lipase in or from heart muscle cells. Experiments will be conducted to alter lipoprotein lipase activity in the heart. These treatments will include food deprivation, food deprivation is Streptozotoxin-induced diabetes, food deprivation followed by refeeding, glucocorticoid administration, adrenalectomy with and without glucocorticoid administration, and hypophysectomy. A major effort will be directed at comparing changes which develop in intracellular lipoprotein lipase activity to concomitant changes in isolated heart myocytes. In addition, isolated myocytes will be incubated in the presence of materials known to effect lipoprotein lipase activity in the heart in order to identify factors which enhance secretion of the enzyme from these cells. A better understanding of these mechanisms will add to our knowledge of lipid metabolism in normal and disease states.